Fuel system for internal combustion engine

ABSTRACT

An internal combustion engine is supplied with combustion air via an inlet manifold. A throttle valve controls the amount of air admitted to the combustion chamber. A fuel injector is provided for injecting liquid fuel into the airflow in the inlet manifold downstream of the throttle valve. A vaporiser is located upstream of the throttle valve. Under light load conditions most if not all of the fuel required by the engine is supplied by the vaporiser. The throttle valve will accordingly be wider open, for any particular power output, than it would be if it controlled only combustion air. At high power outputs (typically after the throttle valve has reached a wide-open state) fuel is supplied by the injector 11 and the output of the vaporiser is reduced so that more air can be admitted to the cylinder for effective combustion of the liquid fuel supplied through the injector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Patent Application No. PCT/GB2005/004132 filed on Oct. 27, 2005, which claims the benefit of GB 0423945.5, filed Oct. 28, 2004. The disclosures of the above applications are incorporated herein by reference.

FIELD

The present disclosure relates to a fuel system for an internal combustion engine, and in particular a fuel system which results in improved economy and/or improved specific power output, which is applicable to both spark ignition (Otto) engines and compression ignition (diesel) engines.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

A gasoline engine works by drawing into its cylinder a mixture of air and fuel which is compressed, then ignited to burn and thus generate power.

In the past the fuel air mixture was provided by a carburettor. Now the fuel system is usually electronically controlled and has one or more injectors which deliver fuel to the manifold and/or cylinder.

It is essential that at the time of ignition a burnable mixture is present in the cylinder near the igniter. As a result the mixture must be controlled to be within ignitable limits. Consequently the volume of air ingested by the engine must be matched to the fuel volume. This is achieved by a throttle valve which limits the intake of air.

The size of engine fitted to almost all cars is such that full power is rarely used and, in particular, in urban traffic the engine is usually operating at a small fraction of its maximum power outlet. Thus the engine is generally operating with the throttle valve partly closed. Consequently the engine suffers significant pumping losses as the air is drawn past this obstruction. This loss is the reason that Otto engines are less economic of fuel than Diesel engines in urban traffic. If this loss could be eliminated Otto engines economy would rise to be close to that of a diesel engine of similar power.

In the past there have been attempts to reduce this loss by supplying the gasoline in vapour form rather than as a liquid. The increased volume of flow then allowed the throttle to be opened wider thus reducing the pumping loss and improving economy. However, supplying the fuel as vapour also limits the maximum amount that can be drawn into the cylinder and hence the maximum power. The economy achieved by fitting a vapouriser to an engine of any given size turns out to be approximately the same as that achieved by fitting a smaller conventionally fuelled engine which has the same maximum power. Consequently vapourisers have been abandoned as economy devices.

SUMMARY

In accordance with the present disclosure there is provided an internal combustion engine comprising: at least one combustion chamber; an inlet manifold for supplying combustion air to the combustion chamber; means for supplying fuel to the combustion chamber, the means for supplying fuel comprising first means for supplying a fuel vapour to the inlet manifold and second means for supplying liquid fuel to the combustion chamber or the inlet manifold; and control means for controlling the first and second fuel supply means so that, under light load conditions, at least some of the fuel supplied to the combustion chamber is supplied by the first means and, under heavy load conditions, the output of the first means is reduced to increase the amount of air supplied to the combustion chamber.

The essence of the new idea is to combine a vapouriser with a conventional fuelling system to provide an Otto engine having economy close to that of a diesel while maintaining the Otto engine maximum power output.

At low power all, or most, of the fuel would be supplied as vapour allowing the throttle to be opened more widely than for a conventionally fuelled engine. As the demand for power increases the throttle valve is progressively opened until full throttle is reached. When more power is required the throttle is maintained fully open, and the supply of vapour is restricted allowing more air to enter the manifold and liquid fuel is supplied in the manifold. This switch from vapour to liquid fuel continues progressively until at maximum power the intake through the throttle is only air and the fuel is supplied entirely as liquid. As a result the throttle is open as wide or wider than that of a conventionally fuelled engine at all times in the cycle and the maximum available power remains the same as in a conventionally fuelled engine. The device could be retro fitted to existing vehicles or incorporated into new designs.

Instead of using the vaporiser entirely for improved economy it could also be set up for increased power. When liquid fuel is supplied not all of it is burned as a result of poor vaporisation and mixing. Supplying vapour in addition to liquid fuel at maximum throttle opening would enhance maximum power providing it only displaced air that would not otherwise react with fuel. In a conventional diesel engines air is admitted to the inlet manifold without a throttle valve, and an appropriate amount of fuel is injected into the hot air in the cylinder after it has been compressed. The fuel quantity and injection pattern is tailored to self ignite the fuel as it mixes with the hot air. As a result such engines do not suffer from throttle pumping losses. However, the compression required to heat the air adequately for self-ignition imposes significant friction losses.

The maximum power output of a diesel engine is limited by smoke formation as the hydrogen in the fuel rapidly burns leaving behind the less reactive carbon in the fuel. This occurs in part as result of the poor fuel air mixing which is intrinsic to the diesel design as the fuel and air do not have long to mix following injection.

A vaporiser could be used to supply additional pre vapourised fuel when high power was demanded. The premixed fuel would burn effectively once ignited by the injected fuel. As a result the maximum available power from the same engine would be increased or fuel economy could be improved if a smaller engine with less friction was used for the required duty.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 illustrates schematically a gasoline fuelled Otto engine incorporating an embodiment to the present disclosure; and

FIG. 2 illustrates schematically a portion of a compression ignition diesel engine incorporating an embodiment to the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

Referring firstly to FIG. 1 there is shown schematically a portion of an internal combustion engine 1. The portion shown comprises a cylinder 2 in which a piston 3 is mounted for reciprocating movement. The piston 3 is connected, in a conventional manner, by means of a conrod (not shown) to a crankshaft. The cylinder 2 is covered by a cylinder head 4 in which is mounted an inlet valve 5 and one or more exhaust valves (not shown). An ignition device, for example a spark plug, 6 is also mounted in the cylinder head. An inlet manifold 7 supplies a gasoline/air mixture to the inlet valve 5. The air 8 for the gasoline/air mixture is derived from a suitable filtered source and the gasoline is derived from a fuel injector 9 and/or a vaporiser 10 as described in more detail hereinafter. A throttle valve 11 is located in the inlet manifold downstream of the vaporiser 10 and upstream of the injection device 9.

In use, under light to medium load conditions fuel for the fuel /air mixture is provided as vaporised gasoline from the vaporiser 10. Accordingly the mixture which is controlled by the throttle valve 11 is a mixture of air and vaporised gasoline. In order to supply sufficient of this mixture to provide a particular power output from the engine the throttle valve 11 will tend to be wider open than it would be if the fuel fraction of the gasoline/air mixture was supplied by a fuel injector located downstream of the throttle valve.

As demand for power from the engine 1 increases the throttle valve 11 is opened progressively until it is fully open. If, thereafter, addition power is required liquid fuel is injected into the manifold 7 through the injector 9 downstream of the throttle valve. If necessary, in order to provide sufficient air for effective combustion of the additional fuel the output of the vaporiser 10 is reduced thereby allowing the mixture which flows through the throttle valve 11 to have a higher air content. At maximum power output it is envisaged that the vaporiser output will have been reduced to zero or close to zero and that the entire fuel requirement for the gasoline/air mixture will be provided by the injector 9.

The exact phasing of the operation of the vaporiser 10 and injector 9 will be determined by the nature of the power requirements for the engine, the particular operating conditions of the engine, and the design of the inlet manifold. In certain applications it may be desirable to start injecting liquid fuel through the injector 9 before the throttle 11 has reached the wide-open position. Under these circumstances it is possible that the output of the vaporiser may be curtailed before wide-open throttle is reached. The critical thing is that during low power output operation of the engine a significant proportion if not all of the required fuel for the gasoline/air mixture supplied to the engine will be derived from the vaporiser thereby allowing the throttle 11 to operate at a relatively wide open configuration for the engine power output and thereby reducing pumping loss normally associated with throttle valves which control only air admission.

Referring now to FIG. 2 there is shown a portion of a diesel engine 21. The engine 21 includes a cylinder 22 in which a piston 23 is mounted for reciprocating movement in conventional manner. Air 28 for the engine is supplied from a suitable filter to an inlet manifold 27. As is conventional for a diesel engine the manifold 27 does not include a throttle valve. An injector 29 is provided for injecting liquid fuel (typically as a spray of droplets) into the combustion chamber of the engine. An inlet valve 25 controls admission of combustion air to the combustion chamber.

In accordance with the present disclosure the engine 21 is provided with a vaporiser 30 which supplies vaporised fuel to the inlet manifold 27. The amount of fuel supplied by the vaporiser 30 is insufficient to result in spontaneous detonation of the fuel/air mixture which is admitted via the inlet manifold 27 as it is compressed by movement of the piston. Detonation will not be initiated until liquid fuel is injected into the combustion chamber via the injector 29 at or close to the top dead centre position of the piston 23. However, once detonation has been initiated the total burn of the fuel contained in the combustion chamber will be quicker and cleaner than would be the case if all the fuel was supplied through the injector 29. Accordingly, the presence of the vaporiser 30 will result in more effective combustion of fuel at low to medium engine power output. As in the case of the embodiment of FIG. 1, at higher engine outputs the output of the vaporiser 30 will be reduced so that a higher portion of the mixture supplied to the combustion chamber by the inlet manifold 27 is air. At the limit, the vaporiser 30 will be inhibited from omitting any vaporised fuel to the inlet manifold 27 so that pure air will be admitted to the combustion chamber through the inlet valve 25 and the entire fuel requirements of the engine will be met by injection of liquid fuel through the injector 29.

It is to be understood that although the disclosure has been described in the context of a single cylinder, the disclosure will be applicable to multi-cylinder engines and, in particular, will be desirable in the case of engines having a wide range of power output requirements. This situation typically arises in internal combustion engines intended for automobiles. The disclosure is not, however, limited to such applications. 

1. An internal combustion engine comprising: at least one combustion chamber; an inlet manifold for supplying combustion air to the combustion chamber; means for supplying fuel to the combustion chamber, the means for supplying fuel comprising first means for supplying a fuel vapor to the inlet manifold and second means for supplying liquid fuel to the combustion chamber or the inlet manifold; and control means for controlling the first and second fuel supply means so that, under light load conditions, at least some of the fuel supplied to the combustion chamber is supplied by the first means and, under heavy load conditions, the output of the first means is reduced to increase the amount of air supplied to the combustion chamber.
 2. The internal combustion engine according to claim 1 including means for controlling the admission of combustion air to the inlet manifold, wherein during a first phase of operation of the engine, power output is increased by progressively opening the combustion air control means and progressively increasing the amount of fuel supplied by the first means, and, during a second phase of operation of the engine, the means for controlling the admission of combustion air is maintained at a constant state and power output is increased by supplying progressively more fuel from the second means.
 3. The internal combustion engine according to claim 2 wherein the substantially constant state is a wide-open throttle state.
 4. The internal combustion engine according to claim 1 wherein the first means is a vaporiser.
 5. The internal combustion engine according to claim 1 wherein the second means is a fuel injector.
 6. The internal combustion engine according to claim 1 wherein the engine is an Otto engine and a throttle valve is located in the inlet manifold downstream of the first means.
 7. The internal combustion engine according to claim 6 wherein the second means is a fuel injector for injecting fuel into one of at least the inlet manifold and the cylinder downstream of the throttle valve. 8 The internal combustion engine according to claim 1 wherein, under light load conditions, substantially all of the fuel supplied to the combustion chamber is supplied by the first means.
 9. The internal combustion engine according to claim 1 wherein the engine is a diesel engine.
 10. The internal combustion engine according to claim 1 wherein at maximum power output all fuel required by the engine is supplied by the second means.
 11. An internal combustion engine comprising: at least one combustion chamber; an inlet manifold for supplying combustion air to the combustion chamber; a fuel supply device for supplying fuel to the combustion chamber, the fuel supply device comprising a first device for supplying a fuel vapor to the inlet manifold and second device for supplying liquid fuel to the combustion chamber or the inlet manifold; and a control device for controlling the first and second fuel supply devices so that, under light load conditions, at least some of the fuel supplied to the combustion chamber is supplied by the first fuel supply device and, under heavy load conditions, the output of the first fuel supply device is reduced to increase the amount of air supplied to the combustion chamber.
 12. The internal combustion engine according to claim 11 including a device for controlling the admission of combustion air to the inlet manifold, wherein during a first phase of operation of the engine, power output is increased by progressively opening the combustion air control device and progressively increasing the amount of fuel supplied by the first fuel supply device, and, during a second phase of operation of the engine, the device for controlling the admission of combustion air is maintained at a constant state and power output is increased by supplying progressively more fuel from the second fuel supply device.
 13. The internal combustion engine according to claim 2 wherein the substantially constant state is a wide-open throttle state.
 14. The internal combustion engine according to claim 11 wherein the first fuel supply device is a vaporiser.
 15. The internal combustion engine according to claim 11 wherein the second fuel supply device is a fuel injector.
 16. The internal combustion engine according to claim 11 wherein the engine is an Otto engine and a throttle valve is located in the inlet manifold downstream of the first fuel supply device.
 17. The internal combustion engine according to claim 16 wherein the second fuel supply device is a fuel injector for injecting fuel into one of at least the inlet manifold and the cylinder downstream of the throttle valve. 18 The internal combustion engine according to claim 11 wherein, under light load conditions, substantially all of the fuel supplied to the combustion chamber is supplied by the first fuel supply device.
 19. The internal combustion engine according to claim 11 wherein the engine is a diesel engine.
 20. The internal combustion engine according to claim 1 wherein at maximum power output all fuel required by the engine is supplied by the second fuel supply device. 